Climate Impacts Group Releases 3-Month PNW Climate Outlook 

Columbia Basin Bulletin

April 6, 2007 

An April update by the University of Washington ’s Climate Impacts Group says the outlook for April-May-June is for a greater than 33 percent chance of warmer than normal temperatures for much of Oregon and Idaho , and equal chances for above, below, or near normal temperatures in northwest Oregon , the northern tip of Idaho and all of Washington .  

Mountain snowpack as of this week is below normal in most of the interior Northwest.  

The near-term precipitation forecast is equal chances for above, below, or near normal precipitation throughout the Pacific Northwest .  

The CIG notes that the forecasts should be interpreted as the tilting of odds towards general categories of conditions, and should not be viewed as a guarantee that the specified conditions will be realized.  

Since mid-January, says the CIG, the weather has been more seasonable.  

For February and March averaged together, temperatures were slightly above the long-term average around much of the Pacific Northwest with more moderate anomalies in southeast Oregon through southern Idaho .  

With the exception of western Washington , precipitation has been below to much below average at most locations in the Pacific Northwest , especially in eastern Oregon .  

Mountain snowpack, which got off to a good start, has not been building well since February and was below average in most of the interior Pacific Northwest as of April 3.  

Basins were reporting at 70-87 percent of average in the Oregon Cascades; 40-72 percent of average in eastern Oregon ; 57-79 percent of average in southern Idaho ; 76-81 percent of average in north Idaho ; 81-99 percent of average in eastern Washington ; and 91-110 percent of average in the Washington Cascades.  

Wasn't the El Niño/Southern Oscillation (ENSO) supposed to bring warmer and drier conditions?  

Generally speaking, warm ENSO conditions in the tropical Pacific often bring the Pacific Northwest a milder, drier winter, but the typical pattern isn't guaranteed.  

CIG says while ENSO is the strongest determinant of how the Northwest winter climate varies from one year to the next, it does not explain even half of how one winter differs from another.  

This year's El Niño, says the CIG, was not accompanied by the persistently shifted storm track and associated patterns of precipitation and temperature changes that have been observed in many past El Niño winters.  

During January, the El Niño event was substantially weakened as an equatorial oceanic Kelvin wave pumped cold water to the surface in the eastern Pacific, leading to a rapid transition to ENSO-neutral conditions.  

Current model forecasts of ENSO from 21 different prediction tools show ENSO possibilities for the next year, with most forecasts suggesting ENSO neutral conditions for the rest of 2007, and about one-third of the forecasts calling for the development of La Niña conditions by summer.  

ENSO forecasts issued in the spring generally have the lowest skill, so CIG says it is prudent to continue monitoring conditions in the tropical Pacific and not place too much emphasis on this latest round of ENSO forecasts. ENSO forecasts issued in the summer and fall have historically been much more accurate than those issued in spring.  

For more information go to http://www.cses.washington.edu/cig/fpt/cloutlook.shtml 

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